A voltage coil is an essential component in the electromagnet section of an electromechanical utility watthour meter. Voltage coils typically comprise three primary elements: a bobbin composed of an electrically inert material, wire capable of generating a magnetic field, and isolated terminal or wire ends. A voltage coil is also encapsulated prior to final testing. The manufacture of conventional voltage coils is labor intensive and these voltage coils are typically not able to handle large voltages; e.g., those on the order of about 8,000 volts.
FIG. 1A shows a top view of a conventional voltage coil. FIG. 1B shows a bottom view (without attached terminals) and FIG. 1C shows a side cross-sectional view of the conventional voltage coil of FIG. 1A. In manufacturing a conventional voltage coil, one end of a wire 5, such as copper, is captured in a terminal, then an operator inserts a terminal 10 into a first or start terminal mounting box 15 that is part of a bobbin 2. The wire 5 is guided around the box 15 and through a slot 17 in an upper flange 20 and wrapped around the core 25 of the bobbin 2 a predetermined number of times or windings. It should be noted that the bobbin 2 also comprises a lower flange 22, and the wire 5 is wound around the core 25 between the upper flange 20 and the lower flange 22.
After the wire has been wound the predetermined number of windings, a piece of tape is applied to keep the wire from unwinding. The wire is again captured in a second or end terminal 30 and the end terminal 30 is then inserted into a second or end terminal mounting box 35. In FIG. 1A, the wire 5 is shown as a dashed line toward its starting and ending points. The voltage coil is then sent for the subsequent steps of testing and encapsulation. The winding of the conventional voltage coil is labor intensive, and has a long manufacture cycle which leads to low productivity and high cost. Also, the encapsulation of the conventional voltage material uses a thermoset material which leads to a long cure time, poor yield, low productivity, and high cost.
U.S. Pat. No. 5,774,036, entitled "Bobbin-Mounted Solenoid Coil and Method of Making", issued to Hrytzak et al., describes a solenoid coil in which a magnet wire (MW) is wrapped around a bobbin core (24) and terminals (84, 86) are inserted into terminal sockets to connect to the magnet wire (MW). The solenoid coil is used in very low voltage applications, such as those in automotive vehicles (about 12 volts), and cannot be used in high voltage or electromagnet applications because the terminals are spaced too close together, thus resulting in the starting and ending points of the wire being close together. It should be noted that a solenoid is different from an electromagnet.
Although the art of voltage coils is well developed, there remain some problems inherent in this technology, particularly the ability for small coils having very fine magnet wire to handle high voltages. Therefore, a need exists for a voltage coil that overcomes the drawbacks of the prior art.